1. Field of the Invention
The present invention relates to a seek routine of a hard disk drive.
2. Background Information
Hard disk drives contain a plurality of magnetic heads that are coupled to rotating disks. The heads write and read information by magnetizing and sensing the magnetic fields of the disk surfaces. Each head is attached to a flexure arm to create a subassembly commonly referred to as a head gimbal assembly (“HGA”). The HGA's are suspended from an actuator arm. The actuator arm has a voice coil motor that can move the heads across the surfaces of the disks.
Information is typically stored in radial tracks that extend across the surface of each disk. Each track is typically divided into a number of segments or sectors. The voice coil motor and actuator arm can move the heads to different tracks of the disks.
FIG. 1 shows a typical track that has a number of fields associated with each sector. A sector may include an automatic gain control (“AGC”) field 1 that is used to adjust the strength of the read signal, a sync field 2 to establish a timing reference for the circuits of the drive, and ID 3 and Gray Code 4 fields to provide sector and track identification.
Each sector may have also a servo field 5 located adjacent to a data field 6. The servo field 5 contains a plurality of servo bits A, B, C and D that are read and utilized in a servo routine to position the head 7 relative to the track. By way of example, the servo routine may utilize the algorithm of ((A-B)−(C-D)) to create a position error signal (“PES”). The PES is used to create a drive signal for the voice coil motor to position the head on the track.
To access data at different disk tracks the drive enters a seek routine. During a seek routine a requested address location is provided and a corresponding seek time and drive current are calculated to drive the voice coil motor and move the heads to the desired location. The temperature of the drive and the voltage provided to the voice coil motor can fluctuate during operation of the disk drive. Variations in temperature and voltage can change the seek time required to move the heads to the desired track location. For example, a low voltage will not move the heads a sufficient distance in a stated seek time. Likewise, an increase in temperature will cause a corresponding increase in the electrical resistance of the voice coil and reduction in the driving current of the VCM. It would be desirable to provide a hard disk drive that accounts for variations in temperature and voltage for a seek routine in the drive.